The popularity of gaseous fuels, such as compressed natural gas (CNG), renewable natural gas (RNG), propane, hydrogen, dimethyl ether (DME), for powering vehicles has increased. Thus, the need to deliver gaseous fuel to vehicles has increased. The infrastructure used to deliver liquid fuels such as gasoline and diesel is not well suited to deliver gaseous fuels. Liquid fuels may be pumped above the tank to be filled, and gravity allows the fuel to flow into the tank. The pumping is the same regardless of how full the tank is, so the first gallon into a tank fills at the same rate as the last gallon into the tank. However, the rate of filling a tank with gaseous fuel depends on the pressure differential between the fuel source and the tank being filled. As the tank fills, the pressure increases, and the fill rate decreases.
Liquid fuel filling stations (gasoline, diesel, etc.) have one pump per dispenser, so the number of dispensers in use doesn't affect the fill rate. Gaseous fuel dispensers do not have pumps as do liquid fuel dispensers, so the fill rate depends on the number of tanks being filled. Also, the fittings and connections used for liquid fuel are not suitable for gaseous fuels.
The description herein uses CNG to refer to compressed natural gas, and most of the background and description is provided using CNG as an exemplary gaseous fuel. However, other gaseous fuels, such as renewable natural gas (RNG), propane, hydrogen, dimethyl ether (DME), biogas, LPG (propane), LNG (liquid natural gas), CNG (compressed natural gas), ANG (absorbed natural gas), Hydrogen 20%+CNG 80% (hythane- or similar % blends), bio-methane, bio-CNG or bioCNG or Biocng, hybrid-combo (combinations of the above and/or electric and or petroleum products could be used, and the invention is not limited to CNG except where CNG is claimed. Also, when “gas” is used herein it refers to gaseous fuel, and gasoline is used to refer to gasoline.
Traditional CNG filling stations include 3 large pressure vessels for storage of the compressed natural gas (CNG) at pressures up to 5000 psi. The storage tanks are filled using one or more compressors that receive natural gas through a pipeline or other storage vessels such as tube trailers, and compress it in the tanks. The storage vessels (each typically 11,000 standard cubic feet SCF) reduce the amount of time it takes to fill a vehicle (typically 80-150 diesel gallon equivalent DGE) by having more CNG volume at higher pressure than the compressing station could normally provide on demand. This typical system has been used for years in the CNG industry but it has deficiencies related to filling time as compared to traditional diesel truck filling times.
Traditional diesel trucks fill at a rate of 20-30 gallons per minute depending on venting options. Equivalent CNG stations using typical NGV2 nozzles (a standard type for natural gas) fill at a rate up to 12 DGE (Diesel Gallon Equivalent) when the filling stations 3 storage vessels are at maximum capacity. However, if a second or third vehicle arrives for filling before the 3 storage vessels are refilled it creates a scenario where the second and third vehicle quickly consume the limited stored pressure and then all of the vehicles being filled wait for the compressors to catchup. This makes the first vehicle wait for an extra-long time to fill up, since one compressor may only produce 265 scfm if the inlet pressure is 30 psi from the pipeline.
Recent improvements have been to provide multiple compressors at each filling station, but there can still be delays. Truckers and other CNG users don't want to wait 10 or 20 minutes to fill up just because additional vehicles show up at the adjacent dispensers. Diesel truckers are used to filling up a 120 gallon tank in 4 minutes. Under ideal conditions it takes 10 minutes to fill a 120 DGE tank with CNG, but with concurrent vehicles filling up, the fill up time can be much longer.
Typical pipe fittings and sub-components sold in any industry have traditionally experienced major flow limitations when “quick-disconnect” junctions are required. This perpetuation has continued into the CNG industry but the flow problem has become amplified because of the extremely high flow rates involved and the desire to fill CNG vehicles as fast as possible.
FIG. 4 shows a prior art CNG filling station with three stored tanks 401-403 at various pressure, depending on the usage. The ideal pressure is up to 5000 psi, but as one or more is depleted their pressure is lessened, and they are referred to typically as High (H), Medium (M), and Low (L) pressure based on their current pressure. If a vehicle is switched onto a bank already in use by a different vehicle, the CNG flows to the less full vehicle, thus the new vehicle typically “steals” all the available gas pressure, leaving the first vehicle with little or no gas flow. A dispenser 407 feeding the first vehicle detects that there is no flow of gas, and will switch that vehicle to the next higher bank. If that happens on the high bank, the vehicle is deemed full and the filling ends, without the vehicle getting a full fill. Problems can also be caused by the dispensers switching banks before or after they have used all of the stored gas that is available to them in that bank. CNG dispensers typically operate strictly on flow rate to determine when to switch between the three banks of stored pressure. However, flowrate is only part of the picture. A system based strictly on flow can be fooled by the gas being delivered by the compressors, which can artificially prolong the time a vehicle spends on a given bank, and clog up the queue. Conversely, a dispenser which is set up to handle “high flow” vehicles may switch between banks too early if a “low flow” or nearly full vehicle connects to the system.
The station of FIG. 4 includes a priority panel 405 that makes the connections between dispenser 407 (as well as an optional dispenser 409) and storage tanks 401-403. A dryer 410 receives gas (usually from an underground utility pipe at a psi at 10-110 psi). A multistage compressor 412 receives the dried gas and provides compressed gas through priority panel 405 to tanks 401-403. A second compressor 412A may be included. Priority panel 405 includes the connections and valves to connect the storage tanks to the compressor and to the dispensers.
Another problem with filling a vehicle tank with arises when the nozzle is connected to the vehicle. A traditional diesel or gasoline filling simply requires the nozzle be inserted into the tank fill opening, and the lever pulled to activate the pump, but CNG requires more operations. The nozzle must be locked onto the vehicle with an air-tight seal, and inserting the nozzle unlocks a lever. The lever is then pulled to open a flow path. A pressure sensor must be activated, an upstream valve is opened, and then gas can flow. There are safety features that create turbulence (non-laminar flow), including a check valve in the vehicle, the valve in the nozzle, two break-away safety points in the hose with safety check valves, and the upstream valve. Accordingly, a nozzle that makes filling a tank with CNG less complex is desirable.
Another problem with filling a vehicle tank arises because CNG requires a safety check valve that prevents CNG from escaping when the nozzle is not connected to the vehicle. Existing check valves create turbulence and a lack of laminar flow because they include sharp edges and changes in direction (of the flowing gas). The turbulence heats the CNG, meaning there is less gas for a given pressure (as the CNG heats it expands). This reduces the fill rate and reduces the amount of CNG (in DGE) in the tank when the fill is completed. Accordingly, a check valve that does not heat the CNG or create turbulence is desired. The valves can be located in the vehicle, or in the nozzle. When in the vehicle they prevent CNG from leaking, and preferably, the valve will have a default position that is closed, and that is only opened when the higher pressure from the storage tanks is applied to the valve.
Thus, an improved filling technique for gaseous fueling that improves the filling rate and reduces filling time is desired.